The invention concerns a method of determining the moment of extinction of an ignition spark of an ignition device for an internal combustion engine. The ignition device has a high voltage transformer having a primary side and a secondary side, of which the primary side is connected to a high voltage source and the secondary side is connected to a spark path to provide the ignition spark and an ignition device for an internal combustion engine. The high voltage transformer is, in particular, a coil having a primary side and a secondary side. A high voltage source is electrically connected to the primary side, and a spark path is electrically connected to the secondary side. The time variation in the primary current flowing on the primary side is measured and subdivided at least into a spark burning phase and a subsequent free-running phase of the high voltage transformer, and the transition from the spark burning phase into the free-running phase is equated to the moment of extinction of the ignition spark. The invention is also directed to an internal combustion engine having such an ignition device.
An aim to seek to achieve reliable ignition and cause firing of the combustible mixture is an ignition spark burning duration which is as long as possible.
Fuel mixtures can be caused to fire with a wide range of different methods. In the case of combustion engines such as, for example, a gas engine, in most cases the mixture is ignited by an ignition spark. There are a number of methods of ignition spark generation, primarily an ignition coil ignition system being used in that case. In that respect, for igniting the fuel mixture, it is primarily the plasma energy introduced by way of the spark passage (ionization and activation energy) that is decisive in terms of the quality of the subsequent combustion process. Besides the level of the ignition spark current, for ignition or firing of the fuel mixture, the ignition spark duration is substantially also decisive. Indirect and direct influences such as, for example, pressure, temperature, mixture composition and flow speeds in the combustion chamber, specifically in the region of the ignition spark plug electrodes or spark path, can considerably influence the ignition spark duration. Thus, determining the ignition spark duration is decisive for assessing the effectiveness of an ignition process. As a possible way of measuring the ignition spark duration, it is possible to employ the direct dependency in relation to the current in the high voltage circuit (secondary current of the ignition coil) which is to be equated to the spark current. Those possible ways of directly measuring the ignition spark duration are not possible with most ignition systems, more especially in the case of central ignition systems where only the primary side of the ignition coils is connected to the ignition system, and no measurement parameters can be passed back from the secondary side.
Some approaches for diagnosis of ignition events are known from the patent literature.
Thus, EP 707 144 A2 (ROBERT BOSCH GMBH) describes the use of a current measuring clip-on instrument for the diagnosis of ignition events. There is provided a first resonant circuit whose resonance frequency is matched to rapid changes in ignition current which occur during the beginning of the ignition spark, and there is a second resonant circuit whose resonance frequency is matched to slow changes in ignition current which occur during the ignition spark burning duration.
WO 1994/027043 (ROBERT BOSCH GMBH) proposes a method of detecting misfires. Here the transformed burning voltage on the primary side is used and a comparison is made with limit values for correct ignition.
FIG. 1 shows an ignition device in accordance with the state of the art. It has a high voltage transformer 3 having a primary side 4 and a secondary side 5. In the present case, the high voltage transformer 3 is in the form of a coil. The primary side 4 is connected to a high voltage source 6 through 9. The individual components of the high voltage source are a dc voltage source 6, a high voltage capacitor 7, a free-running diode 8 and a switching element 9.
The secondary side 5 of the high voltage transformer 3 is connected to a spark path 10 for producing the ignition spark.
FIG. 1 shows an ammeter 11 which is connected to the secondary side 5 of the high voltage transformer 3 and by means of which the secondary current can be measured in relation to ground. It is possible in that way to determine the ignition spark duration. It will be noted, however, that the measurement procedure as shown in FIG. 1 is not possible in by far the most ignition systems as in most ignition systems it is only the primary side 4 of the high voltage transformer 3 that is connected to the ignition system and no measurement parameters whatsoever can be passed back from the secondary side 5.
The methods used at the present time do not provide any information about the spark burning duration itself, but compare a parameter measured at the primary side (for example the burning voltage) to previously detected limit values for a correct ignition process.
Detection of the moment of extinction of the ignition spark is decisive for assessing the effectiveness of an ignition process.
A method of the general kind set forth is to be found in U.S. Pat. No. 6,283,103 B1.